I try do dedodulate a signal, saved in complex64 in a .brut file. I have 2 functions, one to automatically identify the frequencies and the other to demodulate, based on the frequencies detected. Here the code : import numpy as np import matplotlib.pyplot as plt from scipy.signal import find_peaks from tkinter import filedialog def estimate_frequencies(signal, fs, niveau_fsk): fft_result = np.fft.fft(signal) fft_freq = np.fft.fftfreq(len(signal), 1/fs) half_spectrum = fft_result[:len(fft_result)//2] half_freqs = fft_freq[:len(fft_freq)//2] peaks, _ = find_peaks(np.abs(half_spectrum), height=np.max(np.abs(half_spectrum))/10) peaks = peaks[half_freqs[peaks] > 0] important_peaks = np.argsort(-np.abs(half_spectrum[peaks]))[:niveau_fsk] estimated_freqs = half_freqs[peaks[important_peaks]] return estimated_freqs def demodulate_fsk(signal, fs, freqs, symbol_duration): instantaneous_phase = np.angle(signal) instantaneous_frequency = np.diff(instantaneous_phase) * fs / (2.0 * np.pi) decoded_bits = [] step_size = int(symbol_duration * fs) for i in range(0, len(instantaneous_frequency), step_size): segment = instantaneous_frequency[i:i+step_size] mean_freq = np.mean(segment) distances = [abs(mean_freq - f) for f in freqs] decoded_bits.append(np.argmin(distances)) return np.array(decoded_bits) filename = filedialog.askopenfilename(title="Selection d'un fichier IQ") signal = np.fromfile(filename, dtype=np.int16).astype(np.float32).view(np.complex64) fs = 46242 # I use the bandwith of my signal niveau_fsk = 2 symbol_duration = 1 / 19608.5 # Modulation speed = 19608.5 Bd freqs = estimate_frequencies(signal, fs, niveau_fsk) print("Fréquences estimées :", freqs) decoded_bits = demodulate_fsk(signal, fs, freqs, symbol_duration) print(decoded_bits) The problem is that frequencies don't seem to be properly detected, and the demodulation doesn't work as expected (the binary train is wrong). Continue reading...
